1. Field of the Invention
The invention relates to a video endoscope system for fluorescence observation which takes a subject image formed from self fluorescence radiating from a living body under the irradiation of excitation light, an illuminating probe for fluorescence observation for illuminating the subject with the excitation light, and a video endoscope for fluorescence observation. The present disclosure relates subject matter contained in Japanese Patent Application No. 2001-393815 (filed on Dec. 26, 2001), which is expressly incorporated herein by reference in its entirety.
2. Description of the Related Art
Conventionally, it is known that, when ultraviolet light (that is, excitation light) of certain wavelengths is incident on tissue of a living body, fluorescence (that is, self fluorescence) radiates at wavelengths longer than those of the incident excitation light, and that abnormal regions such as cancers and tumors emits self fluorescence of intensities lower than normal regions. Video endoscope systems for fluorescence observation using these phenomena take image of the intensity distribution of the self fluorescence with their image pickup devices and form monochrome images (that is, fluorescence images) which show bright and dark patterns indicating the distribution. Bright areas in the fluorescence images are likely to represent normal regions of the living body.
In a body cavity, hollows and recesses inaccessible to light (reference light and excitation light) emit no self fluorescence, forming dark areas in the fluorescence images. Hence, dark areas in fluorescence images do not necessarily represent abnormal regions. The video endoscope systems for fluorescence observation therefor compare the images (that is, normal images) of the body cavity wall taken under visible light (that is, reference light) with the fluorescence images to identify regions at which luminance ratio of the fluorescence images to the normal images fall short of a predetermined value. Because, such regions must be irradiated with the excitation light and are likely to be abnormal regions.
Hereinafter, a video endoscope system 300 for fluorescence observation having both the function of projecting excitation light and the function of projecting reference light will be described with reference to FIG. 5.
This video endoscope system 300 for fluorescence observation has a video endoscope 310, a fiber probe 320, a light source unit 350, an endoscope processor 340, a personal computer (hereinafter, abbreviated as PC) 330, and a monitor 331. The video endoscope 310 has an ordinary configuration and additionally has an excitation light cut filter arranged in front of its image pickup device. The fiber probe 320 can be inserted into and passed through a forceps channel which is built in and led through an insert part of the video endoscope 310. The light source unit 350 introduces excitation light and reference light to the fiber probe 320 alternately. The endoscope processor 340 processes image signals obtained by the image pickup device of the video endoscope 310 shooting a subject to generate image data frame by frame. The PC 330 synchronizes the generation of image data in the endoscope processor 340 with the switching of the excitation light and reference light in the light source unit 350. The PC 330 also compares image data under the irradiation of the excitation light and that under the irradiation of the reference light, both generated by the endoscope processor 340, and thereby generates image data that shows abnormal regions. The monitor 331 displays the image based on the image data generated by the PC 330.
The light source unit 350 must have at least an excitation light filter for transmitting the excitation light, a reference light filter for transmitting the reference light alone, a mechanism for switching optical paths from a single or two light sources to guide light to any one of the filters, and an optical system for coupling the optical paths having passed through the respective filters and introducing the resultant to the fiber probe 320. Accordingly, the light source device 350 inevitably becomes complicated in structure with an increase in size and weight. As a results there has been a problem of restrictions as to suitable examination sites and the like due to difficult transportation and layout.
Moreover, the optical fiber bundle in the fiber probe 320 is long and easy to break, in case it is made of grass fibers. If this optical fiber bundle is broken, the light from the light source unit 350 can no longer be transmitted to the extremity of the fiber probe 320, failing to illuminate the interior of the body cavity. On the other hand, the individual fibers in the optical fiber bundle are harder to break, in case they are made from plastic than the glass fibers. Such fibers, however, lack heat resistance.
Moreover, among the components of the light emitted from the light source(s), those other than the excitation light and reference light are cut off by the respective filters. Besides, the optical system for coupling the optical paths having passed through the respective filters (for example, a beam combiner) directs only components of the excitation light and reference light to the fiber probe 320, so that only a small fraction of the light emitted from the light source reaches the fiber probe 320. In addition, since the optical fiber bundle by no means achieves an internal transmittance of 100%, the emergent light is attenuated in light quantity as compared to the incident light. For that reason, subjects are often irradiated with insufficient quantity of light. Now, if the light source 351 is boosted in use to obtain sufficient quantity of irradiating light, the lamp life becomes short, causing higher medical costs, as well as the light source 351 generates a large amount of heat dangerously.
Another example of video endoscope systems for fluorescence observation is such that the excitation light and reference light are guided through a light guide fiber bundle which is originally arranged in the video endoscope as an illuminating optical system for normal observation. Even in this case, the light source unit must incorporate the mechanism for introducing the excitation light and reference light to the light guide fiber bundle selectively. This produces the same problems as described above.